1. Field of the Invention
The present invention relates to a structure in which a reservoir unit is fitted within a fuel tank.
2. Description of the Related Art
A fuel tank of a motor vehicle requires a structure for gathering a small quantity of remaining fuel around the suction filter of the fuel pump so that, even if the quantity of the fuel remaining in the fuel tank has become very small, the suction filter of the fuel pump may not be exposed out of the fuel. Previously, as it was the usual practice to form the fuel tank of steel sheets, a fuel tank in which a sub-tank was formed around the suction filter of the fuel pump was manufactured by welding steel sheets formed into a sub-tank.
A resin-built fuel tank is beginning to be used in motor vehicles and the like. A resin-built fuel tank is usually manufactured by blow-molding synthetic resin material. In this case, it is difficult to form a sub-tank in a resin-built fuel tank. In view of this difficulty, an opening is formed in the top face of the resin-built fuel tank, and that opening is utilized for arranging a reservoir unit in the fuel tank.
A fuel tank is deformed dependent on variations in atmospheric temperature and in the quantity of fuel within, and accordingly the distance between its top and bottom varies. The suction filter of the fuel pump needs to be maintained in a position near the bottom of the fuel tank regardless of the deformation of the fuel tank.
To meet this need, the reservoir unit is configured of an upper subunit, a lower subunit and an elastic member. The upper subunit is provided with a plate-shaped portion to block an opening formed in the top face of the fuel tank. The lower subunit is provided with a resin-built reservoir, a fuel filter accommodated in the reservoir and a fuel pump also accommodated in the reservoir. To a plate-shaped portion of the upper subunit are fixed stainless steel shafts extending toward the bottom of the fuel tank. Slots to slidably accept the stainless steel shafts are molded integrally with the reservoir of the lower subunit. The elastic member, positioned between the upper subunit and the lower subunit, presses the lower subunit toward the bottom of the fuel tank.
With this structure, the distance between the upper subunit and the lower subunit varies following the deformation of the fuel tank and the consequent variation in the distance between its top and bottom. The suction filter of the fuel pump is maintained near the inner bottom of the fuel tank to match the deformation of the fuel tank.
In a reservoir unit according to the related art, when a large acceleration or deceleration is applied to the fuel tank, a large force works between the fuel tank and the reservoir unit. When the very large force works between the fuel tank and the reservoir unit, the very large force working on the lower subunit is passed on to the plate-shaped portion of the upper subunit because the conventional reservoir unit uses stainless steel shafts. For this reason, if a very large force works between the fuel tank and the reservoir unit, the plate-shaped portion of the upper subunit may be destroyed. The plate-shaped portion is particularly vulnerable to destruction where it is close to the fixed portions of the stainless steel shafts.
If the plate-shaped portion of the upper subunit of the reservoir unit is destroyed, the air-tightness of the fuel tank will be lost. Therefore, a technique to prevent the plate-shaped portion of the upper subunit from destruction even if too large a force works for the reservoir unit to escape destruction is required. Further is needed a technique to enable the motor vehicle to run as required for ensuring safety even if the reservoir unit is destroyed.